No abstract

Nutritional elements can affect plant susceptibility to plant pathogens, including Botrytis cinerea. We tested the effect of potassium (K) fertilization on gray mold in sweet basil grown in pots, containers, and soil. Increased K in the irrigation water and in the sweet basil tissue resulted in an exponential decrease in gray mold severity. Potassium supplied to plants by foliar application resulted in a significant decrease in gray mold in plants grown with a low rate of K fertigation. Lower K fertigation resulted in a significant increase in B. cinerea infection under semi-commercial conditions. Gray mold severity in harvested shoots was significantly negatively correlated with K concentration in the irrigation solution, revealing resistance to B. cinerea infection as a result of high K concentration in sweet basil tissue. Gray mold was reduced following K foliar application of the plants. In general, there was no synergy between the fertigation and foliar spray treatments. Proper K fertilization can replace some of the required chemical fungicide treatments and it may be integrated into gray mold management for improved disease suppression.

Sweet basil white mould (BWM, Sclerotinia sclerotiorum) and grey mould (BGM, Botrytis cinerea) are important diseases in Israel and other basil-growing regions. The impact of microclimate on BWM and BGM and on plant sensitivity to these diseases was studied. Disease incidence was evaluated in three field experiments, each consisting of 10-12 polyethylene-covered tunnels. BWM and BGM incidences were correlated with air temperature, relative humidity (RH) and soil temperature data. The incidence of BWM was negatively correlated with high (above >25 or >30°C) air temperatures, RH > 50% and RH > 75% and high (>21 or >24°C) soil temperatures. BGM incidence was negatively correlated with high (>25°C) air temperatures and high (>21 or >24°C) soil temperatures, and positively correlated with RH >65% or >75%. Shoots harvested from plants grown in the walk-in tunnels were inoculated with S. sclerotiorum or B. cinerea under controlled conditions. Severity of BWM and BGM on those shoots was negatively correlated with tunnel air temperatures of >25 and >30°C and soil temperatures >18°C. Thus, high temperatures were related to reduced disease incidence and to reduced sensitivity to the pathogens. Experiments involving potted plants revealed that heating only the root zone suppresses canopy susceptibility to BWM and BGM. These findings indicate that the effect of high greenhouse temperatures involves an indirect systemic effect that renders the host less susceptible to disease. This effect was also observed in harvested shoots that were no longer at the high temperatures, and the effect was systemic.